[−][src]Trait futures_core::stream::Stream

#[must_use = "streams do nothing unless polled"]
pub trait Stream {
    type Item;
    fn poll_next(
        self: Pin<&mut Self>, 
        cx: &mut Context
    ) -> Poll<Option<Self::Item>>;
}
[−]

A stream of values produced asynchronously.

If Future<Output = T> is an asynchronous version of T, then Stream<Item = T> is an asynchronous version of Iterator<Item = T>. A stream represents a sequence of value-producing events that occur asynchronously to the caller.

The trait is modeled after Future, but allows poll_next to be called even after a value has been produced, yielding None once the stream has been fully exhausted.

Associated Types

type Item[−]

Values yielded by the stream.

Required methods

fn poll_next(self: Pin<&mut Self>, cx: &mut Context) -> Poll<Option<Self::Item>>[−]

Attempt to pull out the next value of this stream, registering the current task for wakeup if the value is not yet available, and returning None if the stream is exhausted.

Return value

There are several possible return values, each indicating a distinct stream state:

  • Poll::Pending means that this stream's next value is not ready yet. Implementations will ensure that the current task will be notified when the next value may be ready.

  • Poll::Ready(Some(val)) means that the stream has successfully produced a value, val, and may produce further values on subsequent poll_next calls.

  • Poll::Ready(None) means that the stream has terminated, and poll_next should not be invoked again.

Panics

Once a stream is finished, i.e. Ready(None) has been returned, further calls to poll_next may result in a panic or other "bad behavior". If this is difficult to guard against then the fuse adapter can be used to ensure that poll_next always returns Ready(None) in subsequent calls.

Implementations on Foreign Types

impl<'_, S: ?Sized + Stream + Unpin> Stream for &'_ mut S[src][−]

type Item = S::Item

impl<P> Stream for Pin<P> where
    P: DerefMut + Unpin,
    P::Target: Stream, [src][−]

type Item = <P::Target as Stream>::Item

impl<S: ?Sized + Stream + Unpin> Stream for Box<S>[src][−]

type Item = S::Item

impl<S: Stream> Stream for AssertUnwindSafe<S>[src][−]

type Item = S::Item

impl<T: Unpin> Stream for VecDeque<T>[src][−]

type Item = T

Implementors

impl<T> Stream for Receiver<T>

impl<T> Stream for UnboundedReceiver<T>

impl<St: Stream> Stream for InterleavePending<St>

impl<Fut> Stream for FlattenStream<Fut> where
    Fut: Future,
    Fut::Output: Stream, 

impl<Fut: Future> Stream for IntoStream<Fut>

impl<A, B> Stream for Either<A, B> where
    A: Stream,
    B: Stream<Item = A::Item>, 

impl<Fut, S> Stream for FlattenSink<Fut, S> where
    Fut: TryFuture<Ok = S>,
    S: TryStream<Error = Fut::Error>, 

impl<Fut> Stream for TryFlattenStream<Fut> where
    Fut: TryFuture,
    Fut::Ok: TryStream<Error = Fut::Error>, 

impl<I> Stream for Iter<I> where
    I: Iterator, 

impl<T> Stream for Repeat<T> where
    T: Clone, 

impl<St1, St2> Stream for Chain<St1, St2> where
    St1: Stream,
    St2: Stream<Item = St1::Item>, 

impl<T> Stream for Empty<T>

impl<St: Stream> Stream for Enumerate<St>

impl<St, Fut, F> Stream for Filter<St, Fut, F> where
    St: Stream,
    F: FnMut(&St::Item) -> Fut,
    Fut: Future<Output = bool>, 

impl<St, Fut, F, T> Stream for FilterMap<St, Fut, F> where
    St: Stream,
    F: FnMut(St::Item) -> Fut,
    Fut: Future<Output = Option<T>>, 

impl<St> Stream for Flatten<St> where
    St: Stream,
    St::Item: Stream, 

impl<S: Stream> Stream for Fuse<S>

impl<St, F> Stream for Inspect<St, F> where
    St: Stream,
    F: FnMut(&St::Item), 

impl<St, F, T> Stream for Map<St, F> where
    St: Stream,
    F: FnMut(St::Item) -> T, 

impl<Fut: Future> Stream for Once<Fut>

impl<S: Stream> Stream for Peekable<S>

impl<T> Stream for Pending<T>

impl<T, F> Stream for PollFn<F> where
    F: FnMut(&mut Context) -> Poll<Option<T>>, 

impl<St1, St2> Stream for Select<St1, St2> where
    St1: Stream,
    St2: Stream<Item = St1::Item>, 

impl<St: Stream> Stream for Skip<St>

impl<St, Fut, F> Stream for SkipWhile<St, Fut, F> where
    St: Stream,
    F: FnMut(&St::Item) -> Fut,
    Fut: Future<Output = bool>, 

impl<St> Stream for Take<St> where
    St: Stream, 

impl<St, Fut, F> Stream for TakeWhile<St, Fut, F> where
    St: Stream,
    F: FnMut(&St::Item) -> Fut,
    Fut: Future<Output = bool>, 

impl<St, Fut, F> Stream for Then<St, Fut, F> where
    St: Stream,
    F: FnMut(St::Item) -> Fut,
    Fut: Future, 

impl<T, F, Fut, It> Stream for Unfold<T, F, Fut> where
    F: FnMut(T) -> Fut,
    Fut: Future<Output = Option<(It, T)>>, 

impl<St1, St2> Stream for Zip<St1, St2> where
    St1: Stream,
    St2: Stream, 

impl<St: Stream> Stream for Chunks<St>

impl<St> Stream for BufferUnordered<St> where
    St: Stream,
    St::Item: Future, 

impl<St> Stream for Buffered<St> where
    St: Stream,
    St::Item: Future, 

impl<Fut: Future> Stream for FuturesOrdered<Fut>

impl<Fut: Future> Stream for FuturesUnordered<Fut>

impl<S: Stream> Stream for SplitStream<S>

impl<St: Stream + Unpin> Stream for SelectAll<St>

impl<St: Stream + UnwindSafe> Stream for CatchUnwind<St>

impl<St, Fut, F> Stream for AndThen<St, Fut, F> where
    St: TryStream,
    F: FnMut(St::Ok) -> Fut,
    Fut: TryFuture<Error = St::Error>, 

impl<St, E> Stream for ErrInto<St, E> where
    St: TryStream,
    St::Error: Into<E>, 

impl<St, F> Stream for InspectOk<St, F> where
    St: TryStream,
    F: FnMut(&St::Ok), 

impl<St, F> Stream for InspectErr<St, F> where
    St: TryStream,
    F: FnMut(&St::Error), 

impl<St: TryStream> Stream for IntoStream<St>

impl<St, F, T> Stream for MapOk<St, F> where
    St: TryStream,
    F: FnMut(St::Ok) -> T, 

impl<St, F, E> Stream for MapErr<St, F> where
    St: TryStream,
    F: FnMut(St::Error) -> E, 

impl<St, Fut, F> Stream for OrElse<St, Fut, F> where
    St: TryStream,
    F: FnMut(St::Error) -> Fut,
    Fut: TryFuture<Ok = St::Ok>, 

impl<St, Fut, F> Stream for TryFilter<St, Fut, F> where
    St: TryStream,
    Fut: Future<Output = bool>,
    F: FnMut(&St::Ok) -> Fut, 

impl<St, Fut, F, T> Stream for TryFilterMap<St, Fut, F> where
    St: TryStream,
    Fut: TryFuture<Ok = Option<T>, Error = St::Error>,
    F: FnMut(St::Ok) -> Fut, 

impl<St, Fut, F> Stream for TrySkipWhile<St, Fut, F> where
    St: TryStream,
    F: FnMut(&St::Ok) -> Fut,
    Fut: TryFuture<Ok = bool, Error = St::Error>, 

impl<St> Stream for TryBufferUnordered<St> where
    St: TryStream,
    St::Ok: TryFuture<Error = St::Error>, 

impl<S, Item, E> Stream for SinkErrInto<S, Item, E> where
    S: Sink<Item> + Stream,
    S::Error: Into<E>, 

impl<S: Stream, F> Stream for SinkMapErr<S, F>

impl<S, Item, U, Fut, F> Stream for With<S, Item, U, Fut, F> where
    S: Stream + Sink<Item>,
    F: FnMut(U) -> Fut,
    Fut: Future, 

impl<S, Item, U, St, F> Stream for WithFlatMap<S, Item, U, St, F> where
    S: Stream + Sink<Item>,
    F: FnMut(U) -> St,
    St: Stream<Item = Result<Item, S::Error>>, 

impl<S, Item> Stream for Buffer<S, Item> where
    S: Sink<Item> + Stream, 

impl<St: Stream01> Stream for Compat01As03<St>

impl<S, SinkItem> Stream for Compat01As03Sink<S, SinkItem> where
    S: Stream01, 

impl<R: AsyncBufRead> Stream for Lines<R>